The sample preparation system serves for the preparation of a large number of samples that are filled into containers. The empty containers are arranged in a sample rack. To perform the fill operation, an empty container which is closed with a screw cap is picked up with a tool and placed on a load receiver of a balance. Next, the cap is removed and the desired amount of the required substance is filled into the container, with the mass of the substance being measured by the balance. Then, the container is closed with the cap and returned to the sample rack.
This describes the operation in which a rotatable gripper is used. The rotatable gripper is parked in a base station. From there, the rotatable gripper is picked up by the robot arm and moved to the container that is to be fetched. The rotatable gripper takes hold of the container, and the robot arm moves the rotatable gripper with the container to the load receiver, where the container is set down. Next, the rotatable gripper opens the screw cap through a rotating action. Then, the rotating gripper with the cap is temporarily parked at the tool base station and the open container is filled with the desired substances. The filling is performed with a dosage-dispensing device, for example a dispensing head which contains or is connected to a supply of the substance. If the container is to be filled with a plurality of different substances, different dispensing devices will be used which are transported by the robot arm between the container and a dispensing device base station. After the filling process has been concluded, the rotating gripper is picked up again by the robot arm and moved to the container. The cap, which is still held by the rotating gripper, is screwed back onto the container, and the filled container is returned to the sample rack.
Typically, the sample amount dispensed into the container is in the range between 0.5 mg and 5000 mg. The weighing of such a small amount of mass requires a balance of high accuracy.
The sample preparation system is used in a laboratory environment. In the preparation of samples, critical substances are dispensed into a container. These substances must not be contaminated with lubricants.
The existing state of the art offers a variety of rotatable grippers.
Rotatable grippers that hold the cap by means of swivel jaws are disclosed in U.S. Pat. No. 7,836,664 B2, EP 2179758 B1, WO 2008043498 A1 and US 2007/0068117 A1. These rotatable grippers have the disadvantage that the jaws have to be greased with a lubricant, which can lead to contamination of the substances being dispensed. In addition, the jaws are pushed down on the cap by a spring force. Thus, the vertical force of the jaws bears against the cap and thus pushes down on the balance. As the balance is highly sensitive, it is therefore possible that the overload protection device of the balance is triggered, which can lead to a shift of the zero point of the balance. Subsequent measurements could thus be inaccurate.
Other rotatable grippers, which are disclosed in U.S. Pat. No. 7,765,772 B2 and U.S. Pat. No. 5,417,031 A, push down on the screw cap during the closing operation through the elastic force of a spring. This spring force would also act on the load receiver and trigger the overload safety device of the balance.
It is therefore the object of the present invention to provide a rotatable gripper which does not cause contamination and does not activate the overload safety device of the balance.